Execute js code inside a ajax handler function in wordpress

I focused on a wordpress plugin development. In this plugin, I’m trying to design a progress bar that moves according a backend process. After an extensive search, I understood that it is possible by using jquery methods.

From this reference, I wrote following code in plugin’s main php file:

<?php
add_action( 'admin_footer', 'my_action_javascript' );

function my_action_javascript() { ?>
<script type="text/javascript" >
jQuery(document).ready(function($) {

    var element = document.getElementById("myBar"); // It is my bootstrap progress bar
    var width=0; // Initial width (%)
    var add=1; // 1% incrementation variable for progress bar

    var data = {
        'action': 'my_action',
        'whatever': 1234
    };
    
    jQuery.post(ajaxurl, data, function(response) {
        alert('Got this from the server: ' + response);
    });
});
</script> <?php
}

add_action( 'wp_ajax_my_action', 'my_action' );

function my_action() {

$whatever = $_POST['whatever'];

echo $whatever;

wp_die();
}

It works fine, the response shows on alert field. However, when I add following js code into that my_action function:

add_action( 'wp_ajax_my_action', 'my_action' );

function my_action() {

$repeater = 0;
$controller = 0;

for ($i=1; $i <= 4000 ; $i++) { 
    if ($repeater <= 10) {
        $controller++;
        if ($controller == 40) { ?>
            //code starts here
            <script type="text/javascript">
            element.style.width = width + add + "%"; 
            element.innerHTML = width + add + "%";
            width = width+add;  
            </script>
            <?php 
            sleep(1);
            $controller=0;
            $repeater++;
        }
    } else {
        return;
    }
}

wp_die();
}

It doesn’t work. I guess the nature of ajax process in wordpress, the core is waiting for finishes all php codes in function and it doesn’t allow run another js code. So, if I miss some point or there is a better way to achieve this; I would be grateful if you help.